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developerWorks: Introduction to EVMS

"Have you ever stopped to think about how many powerful
storage-related technologies are available for Linux? Consider just
our options for a journaling filesystem: ReiserFS, ext3, XFS, and
JFS. Several years ago, Linux didn't even have a journaling
filesystem. Now, we have plenty of them and find ourselves in the
luxurious position of being able to choose the best filesystem for
our needs. Choice is definitely a good thing.

"Now let's think beyond mere filesystems. Linux's software RAID
capabilities, which have been around for awhile, present another
set of possibilities to the Linux admin (for more information, see
Resources for links to my two-part series on Linux software RAID).
And recently, we've been blessed with Sistina's Linux LVM
technology (logical volume management; see Resources for links to
my two-part LVM series and to download Sistina). LVM allows admins
to manage their storage resources with much greater flexibly than
the traditional method of using static disk partitions. With LVM,
admins can expand and shrink filesystems on running servers and
take advantage of other amazing capabilities, such as filesystem
snapshots.

"So, taken as a whole, Linux has a tremendously rich set of
storage-related technologies. And therein lies the problem; taken
as a whole, we do have some great tools. But try to use several of
these storage technologies together and things become complicated.
For example, let's imagine that we want to create a ReiserFS
filesystem that sits upon an LVM logical volume (so that it can be
dynamically expanded as needed), which in turn sits upon a RAID-1
software RAID volume (in order to provide some protection against
disk failure)..."